The present invention relates to a flexible chain serving as the conveyor chain for a cell-type or bucket conveyor system. The endless conveyor strand having the chain supports a multitude of conveyor buckets successively secured in a row, one after the other, and travels around at least two reversing chain wheels disposed at the ends of the conveyor line. One of the reversing wheels is a driven wheel, and the other wheel functions as a tensioning wheel. A chain bucket conveyor system, in particular, a single or double bucket system, has a central chain arranged in the center in relation to the buckets. It has a multitude of inside flat-iron link plates that are arranged in pairs, parallel with each other, with a mutual crosswise spacing that are disposed parallel and symmetrically relative to the longitudinal axis of the chain. The flat iron inside link plates are connected to each other by two chain bolts extending at a right angle in relation to the longitudinal axis of the chain in one plane, forming an inside chain link in the area of their end sections. Each bolt extends through the two inside link plates of a pair of inside link plates associated with them, as well as through two outer link plates with a substantially L-shaped cross section. Each end of the outer link plate flexibly connects to two inner chain links disposed adjacent to each other, in the longitudinal direction of the chain. The outer link plates form fastening angles for securing the chain on a back wall of the conveyor buckets, or on a holding plate that may replace this back wall. The chain has to be connected by fastening means to the back wall of the conveyor buckets. One leg of each outer link plate extends parallel with the inner link plates, and is penetrated by two chain bolts of two inner chain links. The chain bolts are disposed adjacent to each other, and the two inner chain links are also disposed adjacent to one another. In the installed or assembled condition, the other fastening leg of the outer link extends parallel with the outside of a conveyor bucket back wall, and is then connected using a fastening means such as screws. If, however, only each nth (e.g. each second) potential conveyor bucket location is occupied by a conveyor bucket, it has to be connected with a holding plate or the like, so that each center bolt section of a chain bolt extending between the two inner link plates, and engaging the chain under high load as it runs up on the reversing wheels, has a greater diameter than the two end sections of the bolt disposed in the area of the outer link plate. This center enlargement of the diameter serves not only to reduce the area pressure applied to the highly stressed contact areas (and serves to increase the moment of resistance and thus the bending stiffness as well), but also forms ring-shaped stops of each bolt, against which the respective inner link plates can be placed from the outside during installation, so as to maintain their spaced apart position.
The term xe2x80x9ccell conveyorxe2x80x9d used above relates to a chain bucket system referred to also as an elevator system, and thus is one of the oldest continuous vertical bucket conveyor systems, or inclined bucket conveyor systems, or horizontal swinging bucket conveyor systems for the transport of bulk materials, whose conveying cells or carrying elements are designed as buckets for the bulk material to be conveyed. These buckets are usually made of steel and have a welded or deep-drawn type construction, or of gray cast or aluminum cast, plastic or rubber. They may have different shapes, depending on the type of bulk material to be transported, the shapes being flat, flat rounded, medium-deep, or deep with a plane or curved back wall (see, for examplexe2x80x94DIN 15231-15235; 1541-15245; 2220-12223; 22211-22213). The vertical bucket system has the largest widening (see, e.g., VDI guidelines 2324 for xe2x80x9cvertical bucket conveyor systemxe2x80x9d), which is indispensable, for example, as a continuously operating, vertical conveyor for transporting cement clinker in modern cement production plants.
Central chain-type bucket conveyor systems are designed as single-bucket systems, with a strand or line of buckets. However, they may also be designed as double-bucket conveyor systems. Here, two single-strand central chains, each having buckets, are disposed in a common bucket system housing. Each is jointly driven by only one drive by a driving wheel, mounted on a common shaft, whereas the tensioning wheels are generally mounted on separate shafts because the elongation of the two central chains may vary from one chain to the other, so that the tensioning distances that are independent of each other, are extremely useful for a double-bucket conveyor system.
Chains or belts (ropes, also in the past) are used as elements for pulling the bucket systems, whereby chains or ropes may be arranged in a single, or double strand. If a single strand is used as a central chain, it is arranged in the center, in relation to the bucket back wall. A two or double strand design, in a mirror-symmetrical arrangement relative to the center of the buckets, may be designed either on the bucket back wall, or on their side walls.
The pulling elements are made endless and are guided at the ends of the conveyor line. Thus at the head and foot of the bucket system are rollers, or wheels in the form of chain sprocket wheels, or profiled wheels or drums, and reversed at the head and foot. The bucket conveyor system is generally driven at the head, and the required pre-tensioning of the pulling element takes place at the foot. The reversing elements are generally referred to as reversing wheels, a driving wheel, or a tensioning wheel, regardless of what their fixed design is.
The bulk material to be transported is loaded in the buckets by loading or charging devices, such as feed chutes of swing conveyors or a loading bucket system. It can also be scooped up by the buckets at the foot of the bucket system from the so-called xe2x80x9csumpxe2x80x9d (scooping bucket system), preferably using scooping bucket systems for finely granular bulk materials because the scooping forces, and thus the strain acting on the pulling element and the buckets become very high if bulk material with coarser pieces is transported.
The buckets are emptied either by the force of gravity (slow runner) or by centrifugal force (fast runner), whereby the material is emptied from the buckets by the force of gravity.
Chain bucket conveyor systems have link or flexible chains serving as the pulling elements, whereby the link chains may be designed as chains with round links (round steel chains) or bridge-type chains, which, in conveying technology, are generally employed as hand or load chains on lifting equipment. The link chains, which are known in various designs of construction, are generally considered as being transmission chains, or load chains, as well as conveying chains for chain conveyors.
Bolt chains have the simplest and least costly type of construction of the jointed or flexible chains. As a rule, their link plates (or shackles) directly revolve on chain bolts that are secured (for example by rivets or splints) against displacement in the longitudinal direction.
Bolt chains include roller chains (see, for example DIN 8150) having a plurality of inner and outer link plates per link. Flyer chains (see, for example DIN 8152), as well as draw bank chains without bushings (DIN 8156), or with bushings can be used, (DIN 8157), wherein the flyer chains have a constant diameter throughout, and the diameter of the bolt of the other bolt chain types is generally smaller in the center area of the bolt extending between the inner link plates.
The present invention relates to a flexible chain for a chain bucket system, and in turn, to a single-strand bucket system with a central chain arranged in the center in relation to the buckets. Furthermore, it relates quite generally to cell conveyors even if the cell conveyors are not referred to as xe2x80x9cbucket systemsxe2x80x9d in the narrower definition used in conveying technology. This is the case if the conveying line of a cell conveyor extends horizontally, and the conveyor cells, even if designed in the form of buckets, are secured and not swinging on the pulling element (as it is the case with a pendulum-type bucket system), but are connected with the pulling element in a fixed manner. When the term xe2x80x9cbucket systemxe2x80x9d is used hereinafter, it always relates quite generally to a cell conveyor.
Bolt chains have been known in particular as roller chains from the time of Leonardo da Vinci, more than 500 years ago. They basically have inner and outer chain links, alternating with each other, and each consists of a pair of inner shackles, and a pair of outer shackles, in each case overlapping the two neighboring pairs of inside shackles, and flexibly connected with the latter in the two zones of overlap by a chain bolt extending in the longitudinal direction of the chain, similar to bicycle chains. A complete chain link, as defined above, consists of an inner chain link and an outer chain link.
Apart from the bolt chains, the flexible chains also comprise steel-bushed roller chains, as well as roller chains whose bolts all have a constant diameter as with the flyer chain.
As compared to the bolt chains, the steel-bushed roller chains basically exhibit high resistance to wear because their inner shackles are pressed onto inner bushings that are movably seated on the bolts that are connected with the bolts in a fixed manner, which reduces the area pressure. Steel-bushed roller chains (see, for example DIN 8154 and 8164) are generally designed and used for small pitches. These chains also include xe2x80x9cconveying chains with solid boltsxe2x80x9d both without rollers (DIN 8165; 8167; 8175; 8176) and also with rollers (DIN 8165; 8167; 8176), as well as xe2x80x9cconveying chains with hollow boltsxe2x80x9d with and without rollers (DIN 8168), and xe2x80x9cconveying chains with fastening link platesxe2x80x9d (DIN 8165; 8167; 8168).
Steel-bushed roller chains, with their wear resistant properties, have been recognized as being far superior to bolt-type chains even if they are employed as conveyor chains for chain bucket conveyor systems. They have been employed in the past (i.e. up through the 1970""s and 1980""s) as flexible chains, predominantly in slowly running bucket systems with gravity unloading of the buckets. They were also employed as link chains, designed as round links or round steel chains, used almost exclusively for high-speed systems with unloading of the buckets by centrifugal force. They also have been regularly employed, in the meantime, for high-speed bucket systems and the like.
In chain bucket systems with a central chain, fractures of the center bolt sections (between the inner shackles) have often occurred, in spite of suitable material selection and high manufacturing quality, even if the inner bushings were not, or only partially worn, because of their surface hardening. Surface hardening is used to minimize the wear, on both their outer jackets, which come into engagement with the reversing wheels, and their inner jackets that are engaged with a center segment of the chain bolt.
Attempts have been made to overcome these problems through the use of better and stronger materials. However, this measure did not remedy the situation in any decisive manner. On the contrary, the occurrence of fractures of the inner bushings frequently increased with the selection of high-quality materials.
To explain this surprising phenomenon concerning the extremely troublesome fractures of the inner bushings, it was found that the inner bushings of steel-bushed roller chains cannot withstand the pulses or shocks that occur when the chain runs up on the reversing wheel, especially when they are highly stressed, in relation to braking strength, in spite of the material selection and dimensioning of the chain. This is also in spite of their being adapted by their construction, to alleviate the shocks accordingly. The cause of the failures is assumed to do with a hardening depth of a few millimeters between the hardened areas on the outer jacket, and the inner jacket of the inner bushings. Hardly any tough-elastic (cylindrical) xe2x80x9ccorexe2x80x9d is thus left over, so that the inner bushings are admittedly highly resistant to wear, both on the outside and the inside, yet brittle almost all the way through, and thus sensitive to shocks. Even though the inner bushings of steel-bushed roller chains are smooth, through-extending cylinders, and are free of notches per se, fine notch-like fissures are caused by rough operating conditions. The periodically occurring shock stresses cause numerous fine cracks leading to permanent failures on the hardened, brittle outer and inner areas of the inner bushings, or because only a small tough-elastic xe2x80x9ccore areaxe2x80x9d, remains. However, each event of damage is particularly troublesome, especially for a bucket system employed in a cement production plant, since failures cause substantial production costs, apart from the actual repair costs, and can cause a complete plant shutdown, due to the repair work.
The roller chains (see, for example DIN 8187; 8188), because of their almost unlimited field of application, are generally viewed as the most important chains, even though they represent the most expensive design of the flexible steel chains. Their difference over the steel-bushed roller chains, consists in the reduction of the wear and noise of the hardened and generally ground (protective) rollers supported in the bushings. Their costly manufacture permits high capacities, for example in excess of 1,000 kW for driving chains, as well as high chain speeds of up to 30 meters/s. However, their high cost manufacture and structure often makes them unsuitable (apart from their costs) for rough operating conditions frequently found in the field of conveying technology. Their sliding surfaces, which are produced at great expense, cannot be adequately protected against the penetration of bulk material dust or other contaminants, so that their useful life is shortened due to the high wear. Therefore, they are not economically acceptable.
Because the outer shackles of flexible chains overlap the inside shackles associated with them in the end sections, and are generally close to the outer sides of the inner shackles disposed adjacent to them. Because the chain bolts generally extend largely free of play, and with a relatively close fit through the correspondingly shaped drilled holes or bores provided for passing the shackles there-through, flexible chains have only limited transverse mobility, compared to link chains that can move on all sides. Even though flexible chains are not subjected to any substantial pull when slanted in the transverse direction, they have a good center guidance against migrating sideways. This is a highly desirable design especially for a chain bucket system with a central chain, because the chain is generally guided in a form-locked manner, only on the reversing pulleys, mounted at the ends of the conveyor line.
At least one of the reversing wheels of a bucket chain conveyor system is a chain sprocket wheel. This wheel does not have to be the driving wheel for introducing driving force into the chain or chains acting as the pulling element or elements, even though the driving force is high for a large cell-type conveyor.
Although belt bucket conveyor systems for higher levels of conveyance and streams of conveyed material continue to be very important, quantitatively speaking, because they operate with less noise and more quietly as compared to bucket chain conveyor systems, they are usually not usable for certain individual applications for transporting hot materials (see, for example, xe2x80x9cZement, Kalk, Gipsxe2x80x9d [Cement, Lime, Gypsum], 1974, edition e, pages 176 to 181). Thus, the chain-driven cell conveyors such as a bucket chain conveyor system continues to be of substantial importance. Thus also applies to the chain serving as the pulling element as well as the means for carrying the conveyor cells.
Flexible chains for cell conveyors such as bucket systems have been continuously designed as steel-bushed roller chains (see, for example, DE 35 03 302 CCC2; DE 42 33 550 C2; EP 0 662 924 B, or. for example, the prospectus of RUD Kettenfabrik Rieger and Dietz GmbH and Co./Beumer xe2x80x9cCentral Chain for Heavy-duty Bucket Conveyors Systemsxe2x80x9d dated April 1994), whereby separate fastening angles arranged outside of the outer shackles on the end segments of the bolts are generally associated with each of the chain links. The conveyor cells have to be secured on the chain by means of the fastening angles.
However, steel-bushed conveyor chains where the outer shackles of the chain have an L-shaped cross section, and also serve as the fastening angles are known (see, for example, Bulletin No. 5014, xe2x80x9cRex Elevator and Drag Chainsxe2x80x9dxe2x80x94Cement Industry Chains and Accessories of the Rexnod Corporation, USA May 1996).
However, the fractures of the inner bushings described above still occur with these steel-bushed roller chains. A test wherein steel-bushed chains were replaced by bolt chains did not lead to any satisfactory results, so that the trade world has reluctantly stayed with steel-bushed roller chains, and has thus accepted the drawbacks and costs of these systems.
The present invention provides an improved flexible or jointed conveyor chain for use in very rough operating conditions for bucket systems, having the benefits of a bolt chain versus a steel-bushed roller or roller chain, with a very simple and inexpensive type of construction, and having a substantially increased resistance to wear, with a long useful life over conventional bolt chains. It is substantially more reliable to operate than a bushed roller chain, and has low maintenance. Moreover, the chain can be turned over to prolong its useful life, and is easy to install and dismantle without the need for special tools.
The flexible conveyor chain of the invention provides a hybrid or intermediate design between a classical bolt chain and a bushed roller chain, because no inner bushings, surrounding the center bolt segment are present, a feature typically found in a steel-bushed roller chain. The bolt moreover, is not supported in the shackles as with a conventional bolt chain, as in cylindrical bearing cups pressed into the drilled holes in the shackles, but has pot-shaped outer bushings that are connected in a fixed manner with the outer shackles, as known from bushed chains, if use is made of xe2x80x9cfloatingxe2x80x9d bolts. These bolts are freely rotating with a limited axial mobility in a complete encapsulation of the bushing formed by two outer bushings, and an inner bushing aligned with the outer bushings. The flexible chain of the invention could be called an xe2x80x9couter bushing-type bolt chainxe2x80x9d having many advantages that would be obvious to experts in the field. The structure of the chain is almost as simple, and cost favorable as conventional bolt chains, and substantially simpler and more cost effective than conventional bushed chains. Moreover, the weight per meter is distinctly lower for the same breaking load (e.g. at a breaking load of 1,200 kN, clearly lower than 80 kg/m), and practically no maintenance is required because of the self-lubrication of the encapsulated bearing surfaces. The relatively high wear of conventional bolt chains (as compare to bushed chains) has been substantially reduced by the design of invention. Moreover, no permanent fractures have been experienced in spite of the increased diameter of the bolts, which, is unusual in connection with bolt chains.
Here, the bolts are surface-hardened not only on their outer sides, or in the areas adjacent to the inner sides. The chain bolts are also provided with a very tough-elastic core, especially in the highly stressed contact zones, and also provided with zones where the depth of the hardness varies, and there is no hardness in core areas. Thus, permanent fractures can be avoided with high reliability, in spite of the fact that single segments of the bolts have different diameters.
By employing bolts whose diameter is smaller in the bolt end segments than in the neighboring segments of the bolts disposed closer to the center, a labyrinth seal can be disposed between the segment of a bolt located in the area of an inner shackle, and the final segment of the bolt adjoining the former segment outwardly. Thus, the conveyed material or dust or other contaminants cannot penetrate the area, or such penetration is at least made more difficult, in order to increase the resistance to wear, and thus prolong its useful life. The pot-shaped outer bushings preferably extend, slightly beyond the respective end segment of the bolt, and the inner end of the segments have a greater inside diameter, corresponding with the diameter of the bolt in the segments. Each of the outer bushings are designed so that their inner, annular surfaces are close to the outer side of the respective inner link plate, forming a narrow gap, or are directly adjacent to or resting against the outer surface of the inner plate.
The outer bushings are preferably pot-like or cylindrically shaped, and can be manufactured from low cost tubular semi-finished products. They can be sealed on their free, distal outer ends by covers, pressed or screwed into the ends so as to prevent conveyed material or contaminating substances from penetrating the outer bushings. Moreover, the outer bushings or bearing surfaces of the end segments of the bolts disposed in the bushings are self-lubricated from the ends of the bolts. In order to accomplish this, the inner side of the bottom of a pot-shaped outer bushing or its cover is spaced from the end surface of the respective bolt to form a lubricating chamber that can be filled with a lubricant, such as grease.
A simple installation or dismantling of the system, is possible without requiring any special tools, since the bearing bushings are provided on the inner end segments of their outer jacket surfaces with a slightly larger outside diameter than in the remaining segments, whose outer diameters are equal to the diameters of the bores of the outer shackles formed by the fastening angles. The bolts are provided with a groove extending around their two end segments with a small spacing from their respective faces. A locking ring having radial elasticity, is disposed in each of the grooves, and the outer bushings are provided on their inner jackets with a corresponding groove, that is engaged by the locking ring during the installation, as to provide a simple, detachable assembly.